The present invention relates to the concurrent or sequential application of atomization technology to pressure atomizing a Non-Newtonian liquid in order to form a dispersed phase having a controlled particle size distribution within another liquid, typically immiscible, which forms a continuous phase and to maintain or modify this initial particle size during the subsequent polymerization process in the continuous phase contained in a vessel, using a method to create without mechanical agitation a low shear, controlled (preferably low) turbulence flow pattern within a continuous liquid, by continuously or periodically injecting and preferably recycling a neutral immiscible lighter (less dense) fluid, preferably gas, below the free surface of the continuous phase. In one preferred embodiment the liquid being atomized is a partially polymerized mixture of one or more monomers and is subjected to pressure pulsation upstream the atomizer inlet. In other embodiments of the invention the gas is injected into the reactor to create bubbles either substantially larger or at least an order of magnitude smaller than the average size of the dispersed phase.
The present invention teaches the application of high pressure atomization as the method to disperse an organic phase. It has been proposed to atomize and coat monomer droplets in an aqueous medium to form a suspension (Review article E Vivaldo-Lilma et al., An updated review on suspension polymerization. Ind. Eng. Chem., (36) (1997) of S. Matsumoto et al., A production process for uniform-size polymer particles. J of Chem. Eng. Of Japan, vol. 22, No. 6 1989), using coaxial nozzles and injecting the monomer mixture through the inner nozzle and the coating composition through the outer nozzle. The shell of the resulting coated particle is hardened chemically or physically to form a capsule which may be suspended in water and polymerized. Subsequent to polymerization the outer shell is removed from the polymer. The present invention has eliminated an essential feature of the art, as it does not contemplate the formation of a shell about the monomers.
Comparable encapsulation technology is disclosed in U.S. Pat. No. 4,427,794 issued Jan. 24, 1984 assigned to Bayer A. G. Rather than using coaxial nozzles, the patent teaches an encapsulation medium separate from the continuous aqueous phase. As noted above the present invention has eliminated the essential feature of encapsulation required by this reference.
U.S. Pat. No. 5,061,741 issued Oct. 29, 1991, assigned to Mitsubishi Kasei Corporation discloses a method for preparing oil in water type dispersions. The oil is a monomer or monomer mixture which is not pre-polymerized (i.e. a Newtonian liquid to be atomized). The reference fails to teach or suggest the atomization of a non-Newtonian liquid as required by the present invention. Further the reference fails to teach the application of elevated pressure to atomize the oil (monomer) phase. Additionally, the reference teaches the monomer and continuous phases are at relatively low temperatures not exceeding about 30xc2x0 C. A critical feature of the reference is the use of a disperser plate having nozzles in an annular design. The patent teaches away from the present invention in that a disperser plate having an annular layout for the nozzles is not required and the atomizing nozzles may be uniformly distributed over the disperser or orifice plate.
U.S. Pat. No. 3,922,255 issued Nov. 25, 1975 assigned to Rohm and Haas Company teaches atomizing unpolymerized monomers into a continuous water phase. The monomers are not polymerized and therefore are Newtonian. Further the reference fails to teach applying a pressure pulsation to monomer feed to the atomizers. The reference fails to teach the subject matter of the present invention.
There is a series of patents in the name of Timm, assigned to the Dow Chemicals Company which teach dispersing monomer droplets in a continuous phase by subjecting a jet of a monomer mixture to vibratory excitement. This art includes U.S. Pat. Nos. 4,444,961; 4,666,673; and 4,623,706. The references fail to teach atomization of a non-Newtonian liquid. Further the references fail to teach the application of high pressure to the phase to be atomized. Further the flow rate of the atomized phase of the Timms references appear to be up to an order of magnitude lower during the dispersion process than the flow rate of the present invention.
The present invention further teaches to process polymerize the dispersed phase in a flow pattern in a continuous phase created by gas injection. There is a prior art relating to the injection of gas into a continuous liquid phase in sparging and, less often, surface aeration systems. Mechanically agitated tanks are usually used for this task and the main purpose of these systems is to disperse a gaseous component within a liquid component, (e.g. ethylene gas in liquid styrene) for further processing. Other applications involve high pressure gas injection to aid mechanical agitation/stirring by intensifying the mixing and increasing turbulence level in a stirred tank. All these systems operate in highly turbulent regimes and are equipped with mechanical agitators, (Wessner et al, 2002, Nienow et al 1977, Nienow et al., 1985a, Tatterson 1991, Bujalski 1988, Warmoeskerken et al 1984, Chapman et al, 1983). These references teach the technology based on the principles which are quite opposed to the ones proposed in the present invention in that a low shear, low turbulence flow pattern is created in the reactor by gas injection and no mechanical agitation is required. There are also numerous applications of in situ gas injection to remediate contaminated aquifers or soil matrix, but they serve a totally different purpose and operate also on different principles than process described in the present invention.
The present invention seeks to provide a process to pressure atomize non-Newtonian immiscible liquids into a continuous liquid medium and maintain, improve, or alter (reduce) the dispersed droplet size during the subsequent polymerization process by the controlled recirculation of an inert gas through the continuous liquid medium.
The present invention provides a process comprising pressure atomizing from 0.01 to 60 volume % of a non-Newtonian immiscible liquid having a density xc2x120% of the density of the continuous phase, at a pressure of at least 5 bar, below the free surface of a continuous liquid phase which may be stationary or flowing, contained in a tank, pipe or loop vessel, to produce a dispersion of atomized droplets having at least one controlled average diameter from 0.1 mm to 10 mm and to maintain or modify this initial size distribution during the subsequent polymerization by distributing the dispersed phase in a controlled low turbulence flow pattern, created without mechanical agitation in a continuous phase by continuously or periodically injecting at gauge pressure up to 15 bar into selected parts of the reactor one or more streams of gas inert to the reactor contents having a density lower than the continuous phase and immiscible with the reactor contents and recovering this gas from the top of reactor, above free surface of the continuous phase. Preferably the gas is recycled back to the injection ports of the reactor.
In one preferred embodiment the liquid being atomized is a partially polymerized mixture of one or more monomers and is subjected to instantaneous pressure pulsation Upstream the atomizer inlet.
In other embodiments of the invention the gas is injected into the reactor to create bubbles either substantially larger or at least an order of magnitude smaller than the average size of the dispersed phase.